Abstract: Kriging interpolation methods are widely applied to geological modeling because spatial characteristics of borehole samples are considered by using geostatistics. However, most commonly used Kriging techniques (e.g. the ordinary Kriging method) produce smoothed estimation results, those will lead to an inaccurate regionalization of discontinuous geological stratum around zero value zones, such as pinch-out stratum or stratum with missing segments in some areas. In this paper, a combined indicator-ordinary Kriging method is presented to estimate thicknesses of discontinuous geological stratum. In this method, the estimation of stratum thickness is divided into two steps. Firstly, the indicator Kriging method is used to estimate the distributed area of a geological stratum. Secondly, the ordinary Kriging method is employed to estimate the thicknesses of the geological layer in the distributed area. In addition, a standard error is obtained to evaluate the estimation uncertainty of stratum thickness. The proposed method is applied to estimate the thickness of geological stratum in the Shanghai Yangtze River tunnel project. Through cross validations, the case study shows that the proposed method improves the estimation results by reducing the standard deviation by 15% to 18%, and produces more accurate estimates of thickness of discontinuous geological stratum around zero value zones than that given by the ordinary Kriging method and conventional linear interpolation method.

Key words: indicator Kriging, ordinary Kriging, uncertainty, estimation of geological stratum thickness